U.S. patent application number 12/921090 was filed with the patent office on 2011-01-13 for lithium ion secondary battery and method for producing the same.
Invention is credited to Hideaki Fujita, Yasushi Hirakawa, Kiyomi Kozuki, Yukihiro Okada.
Application Number | 20110008661 12/921090 |
Document ID | / |
Family ID | 41055814 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110008661 |
Kind Code |
A1 |
Kozuki; Kiyomi ; et
al. |
January 13, 2011 |
LITHIUM ION SECONDARY BATTERY AND METHOD FOR PRODUCING THE SAME
Abstract
A lithium ion secondary battery of the invention includes an
electrode structure including an electrode group composed of a
strip-shaped laminate or winding including a positive electrode in
which a positive electrode active material layer is attached to a
positive electrode current collector, a negative electrode, and a
separator; a positive electrode current collector plate including
aluminum foil; and a negative electrode current collector plate
electrically connected to the negative electrode. The positive
electrode has, at one longitudinally extending end edge of the
laminate, a positive electrode current collector-exposed portion
protruding beyond the negative electrode. The positive electrode
current collector plate is electrically connected to the positive
electrode by applying a non-corrosive flux containing a fluoride to
at least one of the positive electrode current collector-exposed
portion and the positive electrode current collector plate, and
then welding the positive electrode current collector plate to the
positive electrode current collector-exposed portion.
Inventors: |
Kozuki; Kiyomi; (Osaka,
JP) ; Hirakawa; Yasushi; (Osaka, JP) ; Okada;
Yukihiro; (Osaka, JP) ; Fujita; Hideaki;
(Kyoto, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Family ID: |
41055814 |
Appl. No.: |
12/921090 |
Filed: |
March 6, 2009 |
PCT Filed: |
March 6, 2009 |
PCT NO: |
PCT/JP2009/001032 |
371 Date: |
September 3, 2010 |
Current U.S.
Class: |
429/94 ;
29/623.1; 29/623.3; 429/163 |
Current CPC
Class: |
H01M 10/058 20130101;
H01M 50/531 20210101; H01M 10/0525 20130101; Y10T 29/49112
20150115; Y10T 29/49108 20150115; Y02E 60/10 20130101; H01M 10/0585
20130101; H01M 10/0587 20130101 |
Class at
Publication: |
429/94 ;
29/623.1; 429/163; 29/623.3 |
International
Class: |
H01M 10/0587 20100101
H01M010/0587; H01M 10/38 20060101 H01M010/38; H01M 2/02 20060101
H01M002/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2008 |
JP |
2008-057913 |
Claims
1-10. (canceled)
11. A lithium ion secondary battery comprising: an electrode
structure comprising an electrode group including a laminate or a
winding of a strip-shaped positive electrode in which a positive
electrode active material layer is attached to a positive electrode
current collector, a strip-shaped negative electrode in which a
negative electrode active material layer is attached to a negative
electrode current collector, and a strip-shaped porous insulating
material disposed between said positive electrode and said negative
electrode; a positive electrode current collector plate; and a
negative electrode current collector plate electrically connected
to said negative electrode; and a battery container housing said
electrode structure, wherein said positive electrode current
collector is aluminum foil, said positive electrode has, at one
longitudinally extending end edge of said laminate, a positive
electrode current collector-exposed portion protruding beyond said
negative electrode, said positive electrode current collector plate
is electrically connected to said positive electrode, by applying
only a non-corrosive flux comprising a fluoride to at least one of
said positive electrode current collector-exposed portion and said
positive electrode current collector plate, and then welding said
positive electrode current collector plate to said positive
electrode current collector-exposed portion, and a portion where
said positive electrode current collector plate and said positive
electrode current collector-exposed portion are welded to each
other comprises only the components of said positive electrode
current collector plate and said positive electrode current
collector, and the components of said non-corrosive flux.
12. The lithium ion secondary battery in accordance with claim 11,
wherein said fluoride contains aluminum and potassium.
13. The lithium ion secondary battery in accordance with claim 11,
wherein said flux contains a eutectic of KF and AlF.sub.3.
14. The lithium ion secondary battery in accordance with claim 11,
wherein said negative electrode has, at the other longitudinally
extending end edge of said laminate, a negative electrode current
collector-exposed portion protruding beyond said positive
electrode, and said negative electrode current collector plate is
welded to said negative electrode current collector-exposed
portion.
15. The lithium ion secondary battery in accordance with claim 11,
wherein said positive electrode current collector plate is an
aluminum plate.
16. A method for producing a lithium ion secondary battery
comprising the steps of: (1) laminating or winding a strip-shaped
positive electrode in which a positive electrode active material
layer is attached to a positive electrode current collector
comprising aluminum foil and having a positive electrode current
collector-exposed portion at one longitudinally extending end edge
thereof, a strip-shaped negative electrode in which a negative
electrode active material layer is attached to a negative electrode
current collector, and a strip-shaped porous insulating material,
in such a manner that said porous insulating material is disposed
between said positive electrode and said negative electrode, and
said positive electrode current collector-exposed portion protrudes
beyond said negative electrode, to obtain an electrode group; (2)
applying only a non-corrosive flux comprising a fluoride to at
least one of said positive electrode current collector-exposed
portion and a positive electrode current collector plate comprising
an aluminum plate; (3) welding, after said step (2), said positive
electrode current collector plate to said positive electrode
current collector-exposed portion, thereby electrically connecting
said positive electrode current collector plate to said positive
electrode; (4) electrically connecting a negative electrode current
collector plate to said negative electrode; and (5) housing, in a
battery container, an electrode structure comprising said electrode
group, and said positive electrode current collector plate and said
negative electrode current collector plate respectively welded to
said electrode group.
17. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein said fluoride contains aluminum
and potassium.
18. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein said flux contains a eutectic of
KF and AlF.sub.3.
19. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein said negative electrode has a
negative electrode current collector-exposed portion at one
longitudinally extending end edge thereof, in said step (1), said
positive electrode, said negative electrode, and said porous
insulating material are laminated or wound in such a manner that
said negative electrode current collector-exposed portion protrudes
beyond said positive electrode, and, in said step (4), said
negative electrode current collector plate is welded to said
negative electrode current collector-exposed portion.
20. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein said positive electrode current
collector plate is an aluminum plate.
21. The lithium ion secondary battery in accordance with claim 11,
wherein said fluoride contains aluminum and cesium.
22. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein said fluoride contains aluminum
and cesium.
23. The method for producing a lithium ion secondary battery in
accordance with claim 16, wherein, in said step (3), said positive
electrode current collector plate is abutted on said positive
electrode current collector-exposed portion, and then said positive
electrode current collector plate is heated from above the surface
thereof opposite the surface thereof abutting on said positive
electrode current collector-exposed portion, by using a non-contact
heat source.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lithium ion secondary
battery having a tabless structure in which current collector
plates are welded to current collector-exposed portions provided at
end edges of electrodes, and a method for producing the same.
BACKGROUND ART
[0002] In order to increase the output of a lithium ion secondary
battery, a method has been used in which the current collecting
structure of the electrode group of the lithium ion secondary
battery is configured as a tabless structure. The tabless structure
is described below. An electrode group is formed by winding a
laminate including a positive electrode composed of a positive
electrode current collector and a positive electrode active
material layer attached to the positive electrode current
collector, a negative electrode composed of a negative electrode
current collector and a negative electrode active material layer
attached to the negative electrode current collector, and a
separator disposed between the positive electrode and the negative
electrode. The positive electrode has, at one longitudinally
extending end edge of the laminate, a portion where the positive
electrode current collector is exposed (positive electrode current
collector-exposed portion). The negative electrode has, at the
other longitudinally extending end edge of the laminate, a portion
where the negative electrode current collector is exposed (negative
electrode current collector-exposed portion). The positive
electrode current collector plate is welded to the positive
electrode current collector-exposed portion, whereby the positive
electrode is electrically connected to the positive electrode
current collector plate. The negative electrode current collector
plate is welded to the negative electrode current collector-exposed
portion, whereby the negative electrode is electrically connected
to the negative electrode current collector plate. Consequently, a
current collection path is ensured for the strip-shaped
electrodes.
[0003] Further improvements for the tabless structure have been
investigated. For example, Patent Document 1 proposes providing a
current collector plate with a portion into which a current
collector-exposed portion can bite, and welding the current
collector plate to the current collector-exposed portion with a
part of the current collector-exposed portion biting into that
portion to achieve improved contact between the current collector
plate and the electrode. However, since aluminum foil is used as
the positive electrode current collector of lithium ion secondary
batteries, the positive electrode current collector-exposed portion
cannot be easily wetted by the molten metal from the positive
electrode current collector plate at the time of welding, making it
difficult to achieve good bonding. Consequently, the bonding area
and the bonding strength between the positive electrode current
collector-exposed portion and the positive electrode current
collector plate cannot be provided sufficiently, which may result
in deteriorated output characteristics of the battery and reduced
reliability against vibrations and falling.
[0004] Patent Document 2 proposes applying a brazing material to a
current collector plate in advance, abutting the surface of the
current collector plate to which the brazing material has been
applied on a current collector-exposed portion, and welding the
current collector plate to the electrode at this abutment portion
to reliably bond the current collector plate to the current
collector-exposed portion made of aluminum foil. However, metal
components contained in the brazing material other than aluminum
may be mixed in the welded portion at the time of welding, and
these components may further enter into the battery structure,
adversely affecting the battery characteristics.
[0005] Patent Document 1: Japanese Patent No. 3738166
[0006] Patent Document 2: Japanese Laid-Open Patent Publication No.
2001-93505
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0007] Therefore, it is an object of the present invention to
provide a highly reliable lithium ion secondary battery having
excellent output characteristics, and a method for producing the
same in order to solve the above-described conventional
problems.
Means for Solving the Problem
[0008] A lithium ion secondary battery according to the present
invention includes:
[0009] an electrode structure including an electrode group
including a laminate or a winding of a strip-shaped positive
electrode in which a positive electrode active material layer is
attached to a positive electrode current collector, a strip-shaped
negative electrode in which a negative electrode active material
layer is attached to a negative electrode current collector, and a
strip-shaped porous insulating material disposed between the
positive electrode and the negative electrode; a positive electrode
current collector plate; and a negative electrode current collector
plate electrically connected to the negative electrode; and
[0010] a battery container housing the electrode structure,
[0011] wherein the positive electrode current collector is aluminum
foil,
[0012] the positive electrode has, at one longitudinally extending
end edge of the laminate, a positive electrode current
collector-exposed portion protruding beyond the negative electrode,
and
[0013] the positive electrode current collector plate is
electrically connected to the positive electrode by applying a
non-corrosive flux including a fluoride to at least one of the
positive electrode current collector-exposed portion and the
positive electrode current collector plate, and then welding the
positive electrode current collector plate to the positive
electrode current collector-exposed portion.
[0014] Preferably, the fluoride contains aluminum and
potassium.
[0015] Preferably, the flux contains a eutectic of KF and
AlF.sub.3.
[0016] Preferably, the negative electrode has, at the other
longitudinally extending end edge of the laminate, a negative
electrode current collector-exposed portion protruding beyond the
positive electrode, and the negative electrode current collector
plate is welded to the negative electrode current collector-exposed
portion.
[0017] Preferably, the positive electrode current collector plate
is an aluminum plate.
[0018] Furthermore, the present invention relates to a method for
producing a lithium ion secondary battery including the steps
of:
[0019] (1) laminating or winding a strip-shaped positive electrode
in which a positive electrode active material layer is attached to
a positive electrode current collector including aluminum foil and
having a positive electrode current collector-exposed portion at
one longitudinally extending end edge thereof, a strip-shaped
negative electrode in which a negative electrode active material
layer is attached to a negative electrode current collector, and a
strip-shaped porous insulating material, in such a manner that the
porous insulating material is disposed between the positive
electrode and the negative electrode, and the positive electrode
current collector-exposed portion protrudes beyond the negative
electrode, to obtain an electrode group;
[0020] (2) applying a non-corrosive flux including a fluoride to at
least one of the positive electrode current collector-exposed
portion and a positive electrode current collector plate;
[0021] (3) welding, after the step (2), the positive electrode
current collector plate to the positive electrode current
collector-exposed portion, thereby electrically connecting the
positive electrode current collector plate to the positive
electrode;
[0022] (4) electrically connecting a negative electrode current
collector plate to the negative electrode; and
[0023] (5) housing, in a battery container, an electrode structure
including the electrode group, and the positive electrode current
collector plate and the negative electrode current collector plate
respectively welded to the electrode group.
[0024] Preferably, the fluoride contains aluminum and
potassium.
[0025] Preferably, the flux contains a eutectic of KF and
AlF.sub.3.
[0026] Preferably, the negative electrode has a negative electrode
current collector-exposed portion at one longitudinally extending
end edge thereof; in the step (1), the positive electrode, the
negative electrode, and the porous insulating material are
laminated or wound in such a manner that the negative electrode
current collector-exposed portion protrudes beyond the positive
electrode; and, in the step (4), the negative electrode current
collector plate is welded to the negative electrode current
collector-exposed portion.
[0027] Preferably, the positive electrode current collector plate
is an aluminum plate.
EFFECT OF THE INVENTION
[0028] The present invention can provide a highly reliable lithium
ion secondary battery having excellent output characteristics, and
a method for producing the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a schematic vertical cross-sectional view of a
lithium ion secondary battery according to one embodiment of the
present invention.
[0030] FIG. 2 is a perspective view of the electrode structure
shown in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] The present invention relates to a lithium ion secondary
battery including: an electrode structure including an electrode
group including a laminate or a winding of a strip-shaped positive
electrode in which a positive electrode active material layer is
attached to a positive electrode current collector, a strip-shaped
negative electrode in which a negative electrode active material
layer is attached to a negative electrode current collector, and a
strip-shaped porous insulating material disposed between the
positive electrode and the negative electrode; a positive electrode
current collector plate; and a negative electrode current collector
plate electrically connected to the negative electrode; and a
battery container housing the electrode structure. The invention is
characterized in that the positive electrode current collector is
aluminum foil, the positive electrode has, at one longitudinally
extending end edge of the laminate, a positive electrode current
collector-exposed portion protruding beyond the negative electrode,
and the positive electrode current collector plate is electrically
connected to the positive electrode, by applying a non-corrosive
flux including a fluoride to at least one of the positive electrode
current collector-exposed portion and the positive electrode
current collector plate, and then welding the positive electrode
current collector plate to the positive electrode current
collector-exposed portion.
[0032] This ensures good contact between the positive electrode for
which aluminum foil is used as the positive electrode current
collector and the positive electrode current collector plate, thus
yielding a highly reliable lithium ion secondary battery having
excellent output characteristics.
[0033] When the electrode group is a winding, this positive
electrode current collector plate is disposed so as to cover a
plane substantially perpendicular to the winding axis of the
electrode group. The non-corrosive flux is applied to at least one
of the portion of the positive electrode current collector-exposed
portion that is welded to the positive electrode current collector
plate and the portion of the positive electrode current collector
plate that is welded to the positive electrode current
collector-exposed portion.
[0034] An example of the current collecting structure on the
negative electrode side (the form of connection between the
negative electrode and the negative electrode current collector
plate) described above is the same structure (tabless structure) as
that on the positive electrode side. Specifically, the
above-described negative electrode has, at the other longitudinally
extending end edge of the laminate, a negative electrode current
collector-exposed portion protruding beyond the positive electrode,
and the negative electrode current collector plate is welded to the
negative electrode current collector-exposed portion. When the
electrode group is a winding, this negative electrode current
collector plate is disposed so as to cover a plane substantially
perpendicular to the winding axis of the electrode group.
[0035] Alternatively, a lead-shaped negative electrode current
collector plate may be used as the negative electrode current
collector plate. Specifically, the strip-shaped negative electrode
may have a structure such that it has a negative electrode current
collector-exposed portion along one widthwise end edge, and the
lead-shaped negative electrode current collector plate is welded to
the negative electrode current collector-exposed portion. The
lead-shaped negative electrode current collector plate is disposed
in the width direction of the negative electrode (along the winding
axis of the electrode group).
[0036] The thickness of the aluminum foil used as the positive
electrode current collector may be 10 to 30 .mu.m, for example.
[0037] To achieve excellent current collection capability and
chemical stability under use conditions of lithium ion secondary
batteries, it is preferable to use an aluminum plate as the
positive electrode current collector plate. The thickness of the
aluminum plate may be 0.3 to 1 mm, for example.
[0038] A method for producing a lithium ion secondary battery
according to the present invention includes the steps of:
[0039] (1) laminating or winding a strip-shaped positive electrode
in which a positive electrode active material layer is attached to
a positive electrode current collector including aluminum foil and
having a positive electrode current collector-exposed portion at
one longitudinally extending end edge thereof, a strip-shaped
negative electrode in which a negative electrode active material
layer is attached to a negative electrode current collector, and a
strip-shaped porous insulating material, in such a manner that the
porous insulating material is disposed between the positive
electrode and the negative electrode, and the positive electrode
current collector-exposed portion protrudes beyond the negative
electrode, to obtain an electrode group;
[0040] (2) applying a non-corrosive flux including a fluoride to at
least one of the positive electrode current collector-exposed
portion and a positive electrode current collector plate;
[0041] (3) welding, after the step (2), the positive electrode
current collector plate to the positive electrode current
collector-exposed portion, thereby electrically connecting the
positive electrode current collector plate to the positive
electrode;
[0042] (4) electrically connecting a negative electrode current
collector plate to the negative electrode; and
[0043] (5) housing, in a battery container, an electrode structure
including the electrode group, and the positive electrode current
collector plate and the negative electrode current collector plate
respectively welded to the electrode group.
[0044] When the negative electrode has the same structure as that
of the positive electrode (a structure corresponding to the tabless
structure), or in other words, when the negative electrode has a
negative electrode current collector-exposed portion at one
longitudinally extending end edge thereof, the positive electrode,
the negative electrode, and the separator are laminated or wound in
such a manner that the negative electrode current collector-exposed
portion protrudes beyond the positive electrode in the step (1),
and the negative electrode current collector plate is welded to the
negative electrode current collector-exposed portion in the step
(4).
[0045] An example of forming a laminate is a method in which a
separator made of a porous resin film is disposed between the
positive electrode and the negative electrode as an insulating
material at the time of forming the laminate. Another example is a
method in which a porous resin layer is formed as an insulating
material on one of the positive electrode and the negative
electrode prior to the lamination, and one of the positive
electrode and the negative electrode on which the porous resin
layer is formed is laminated on the other of the positive electrode
and the negative electrode.
[0046] Hereinafter, one embodiment of the lithium ion secondary
battery according to the present invention is described with
reference to FIGS. 1 and 2. FIG. 1 is a schematic vertical
cross-sectional view of a cylindrical lithium secondary battery.
FIG. 2 is a schematic perspective view of the electrode
structure.
[0047] As shown in FIG. 1, the electrode structure is housed in a
battery container 4 composed of a cylindrical battery can 5 having
a bottom and also serving as a negative electrode terminal, and a
battery cover 6 also serving as a positive electrode terminal. The
electrode structure is composed of a columnar electrode group 10
formed by winding a laminate of a positive electrode 1, a negative
electrode 2, and a separator 3 disposed between the positive
electrode 1 and the negative electrode 2, a disc-shaped positive
electrode current collector plate 8 electrically connected to the
positive electrode 1, and a disc-shaped negative electrode current
collector plate 9 electrically connected to the negative electrode
2. The positive electrode current collector plate 8 and the
negative electrode current collector plate 9 are both disposed so
as to cover planes (flat portions 11a and 12a that will be
described below) substantially perpendicular to the winding axis of
the electrode group 10. Furthermore, separators 3 are disposed on
the outermost circumference side and on the innermost circumference
side of the electrode group.
[0048] One end of a positive electrode connector piece 8a is
connected to the positive electrode current collector plate 8, and
the other end of the positive electrode connector piece 8a is
connected to the bottom surface of the battery cover 6. Thereby,
the positive electrode 1 is electrically connected to the battery
cover 6. One end of a negative electrode connector piece 9a is
connected to the negative electrode current collector plate 9, and
the other end of the negative electrode connector piece 9a is
connected to the inner bottom surface of the battery can 5.
Thereby, the negative electrode 2 is electrically connected to the
battery can 5. The end portion of the opening of the battery can 5
is crimped onto the peripheral edge of the battery cover 6 with a
ring-shaped resin sealing body 7 interposed therebetween, and
thereby the electrode structure is housed in the battery container
4 in a hermetically sealed manner.
[0049] The positive electrode 1 is composed of a positive electrode
current collector 1b made of aluminum foil, and positive electrode
active material layers 1a formed on both sides of the positive
electrode current collector 1b. The positive electrode active
material layer 1a may be composed of, for example, a mixture of a
positive electrode active material, a conductive material, and a
binder. For example, a lithium-containing composite oxide such as
LiNiO.sub.2, LiCoO.sub.2, or LiMn.sub.2O.sub.4 may be used as the
positive electrode active material. It is also possible to use an
oxide in which Ni, Co, or Mn in such oxides is partially
substituted with another transition metal. For example, a carbon
material such as acetylene black may be used as the conductive
material. For example, polyvinylidene fluoride may be used as the
binder.
[0050] The positive electrode 1 has, at one end edge of the
positive electrode 1 extending in the longitudinal direction of the
laminate (the upper end edge of the positive electrode 1 in FIG.
1), a portion where the positive electrode active material layer 1a
is not formed, that is, a portion where the positive electrode
current collector 1b is exposed (positive electrode current
collector-exposed portion 11). The positive electrode current
collector-exposed portion 11 protrudes upward beyond the negative
electrode 2 along the winding axis, and the end edge of the
positive electrode current collector-exposed portion 11 is bent in
a direction substantially perpendicular to the winding axis and
inward toward the center of the axis, thus forming a flat portion
11a, which will be a portion welded to the positive electrode
current collector plate 8 as described below. The positive
electrode current collector plate 8 is welded to the end edge (flat
portion 11a) of the positive electrode current collector-exposed
portion 11 to which a non-corrosive flux containing a fluoride is
applied, whereby the positive electrode current collector plate 8
is electrically connected to the positive electrode 1.
[0051] A flux is used as a fusing agent for welding for the purpose
of removing an oxide film formed on the metal surface of a welded
portion and preventing the formation of such an oxide film. An
oxide film on the surface of aluminum foil is dissolved and removed
by the flux that has been melted by heating during welding. This
significantly improves the wettability of the molten metal from the
current collector plate to the aluminum foil, and can thus achieve
a favorable welding state between the positive electrode current
collector plate and the flat portion of the positive electrode
current collector-exposed portion, making it possible to provide a
welding area and welding strength that are sufficient to attain a
good state of bonding of the positive electrode current collector
plate to the positive electrode.
[0052] When a corrosive flux (for example, a flux containing a
chloride) is used, it is necessary to perform a treatment to remove
the remaining flux components after welding for the purpose of
preventing corrosion of the welded portion. However, according to
the present invention, it is not necessary to remove the remaining
flux components since the present invention uses a non-corrosive
flux.
[0053] According to the present invention, since it is not
necessary to use a brazing material for welding the positive
electrode current collector plate and the positive electrode
current collector-exposed portion, the components contained in a
brazing material will not adversely affect the battery, making it
possible to provide a highly reliable battery.
[0054] The fluoride may contain, for example, aluminum, potassium,
or cesium. It is preferable that the fluoride contains aluminum and
potassium because of their excellent non-corrosive properties and
non-hygroscopic properties. Examples of the fluoride include
KAlF.sub.4, K.sub.2AlF.sub.5, K.sub.3AlF.sub.6, AlF.sub.3, KF, and
CsF. These may be used singly or in combination of two or more.
Examples of the non-corrosive flux include a flux containing
AlF.sub.3 and KF, a flux containing KAlF.sub.4 and
K.sub.3AlF.sub.6, and a flux containing KF, AlF.sub.3, and
Al.sub.2O.sub.3.
[0055] It is preferable to use "NOCOLOK" (registered trademark) as
the flux. The amount of "NOCOLOK" applied to the positive electrode
current collector-exposed portion may be 0.1 to 0.3 g/cm.sup.2, for
example. "NOCOLOK" is a flux having a eutectic composition of KF
and AlF.sub.3, and has a eutectic point of 560 to 570.degree. C.
Therefore, when an aluminum plate is used as the positive electrode
current collector plate, the temperature at which the positive
electrode current collector plate is welded to the flat portion of
the positive electrode current collector-exposed portion is
preferably 570 to 660.degree. C.
[0056] Although the flux remains on the surface of the portion
where the positive electrode and the positive electrode current
collector plate are welded to each other, the flux will not
adversely affect the battery characteristics since it is
non-corrosive. "NOCOLOK" has excellent corrosion resistance, and
therefore "NOCOLOK" remaining on the surface improves the corrosion
resistance of the portion where the positive electrode current
collector plate and the flat portion of the positive electrode
current collector-exposed portion are welded to each other.
[0057] The negative electrode 2 is composed of a negative electrode
current collector 2b and negative electrode active material layers
2a formed on both sides of the negative electrode current collector
2b. For example, copper foil may be used as the negative electrode
current collector 2b. The negative electrode active material layer
2a may be composed of, for example, a mixture of a negative
electrode active material, a conductive material, and a binder. For
example, a carbonaceous material such as graphite, petroleum coke,
or carbon fiber, or a metal or oxide capable of absorbing and
desorbing lithium may be used as the negative electrode active
material. For example, a carbon material such as artificial
graphite may be used as the conductive material. For example,
polyvinylidene fluoride may be used as the binder.
[0058] The negative electrode 2 has, at the other end edge of the
negative electrode 2 extending in the longitudinal direction of the
laminate (the lower end edge in FIG. 1), a portion where the
negative electrode active material layer 2a is not formed, that is,
a portion where the negative electrode current collector 2b is
exposed (negative electrode current collector-exposed portion 12).
The negative electrode current collector-exposed portion 12
protrudes downward beyond the positive electrode 1 along the
winding axis, and the end edge of the negative electrode current
collector-exposed portion 12 is bent in a direction substantially
perpendicular to the winding axis and inward toward the center of
the axis, thus forming a flat portion 12a, which will be a portion
welded to the negative electrode current collector plate 9. The
negative electrode current collector plate 9 is welded to the flat
portion 12a of the negative electrode current collector-exposed
portion 12, whereby the negative electrode current collector plate
9 is electrically connected to the negative electrode 2.
[0059] For example, a microporous film made of polyethylene or
polypropylene may be used as the separator 3.
[0060] The electrode group 10 includes an electrolyte. The
electrolyte is composed of a non-aqueous solvent and a lithium salt
dissolved in the non-aqueous solvent. For example, ethylene
carbonate, propylene carbonate, dimethyl carbonate, or ethylmethyl
carbonate may be used as the non-aqueous solvent. For example,
lithium hexafluorophosphate, lithium perchlorate, or lithium
tetrafluoroborate may be used as the lithium salt.
[0061] Hereinafter, a description is given of a specific example of
a production method of an electrode structure composed of the
electrode group 10, the positive electrode current collector plate
8, and the negative electrode current collector plate 9.
[0062] Before forming a laminate (before forming the flat portion
11a), a slurry prepared by dispersing a flux in water is applied to
the end edge (the portion where the flat portion 11a is to be
formed) of the positive electrode current collector-exposed portion
11. Thereafter, water is removed by thermal drying to form a
flux-coated layer on the end edge of the positive electrode current
collector-exposed portion. Alternatively, a flux-coated layer may
be formed by applying the above-described slurry to the flat
portion 11a after forming the flat portion 11a.
[0063] An appropriate amount of a binder such as carboxymethyl
cellulose, polyethylene oxide, polyacrylic acid, or starch may be
further added to the above-described slurry.
[0064] Apart from the above-described slurry, it is possible to use
a slurry prepared by dispersing a flux in an organic solvent.
Examples of the organic solvent include aliphatic hydrocarbons such
as hexane and aromatic hydrocarbons such as toluene. An appropriate
amount of a binder such as polyvinyl butyral, polyvinyl
pyrrolidone, or polystyrene may be further added to such a
slurry.
[0065] The positive electrode 1, the negative electrode 2, and the
separator 3 are laminated in such a manner that the separator 3 is
disposed between the positive electrode 1 and the negative
electrode 2, the positive electrode current collector-exposed
portion 11 protrudes beyond the negative electrode 2, and the
negative electrode current collector-exposed portion 12 protrudes
beyond the positive electrode 1, to form a laminate, which is
further wound to yield an electrode group 10. After the electrode
group 10 is inserted into a cylindrical molding tool having a
bottom, the electrode group 10 is pressed in the direction of the
winding axis from the opening of the molding tool using a specific
pressing tool. At this time, the end edges of the positive
electrode current collector-exposed portion 11 and the negative
electrode current collector-exposed portion 12 are elastically
deformed so as to be bent, thus forming flat portions 11a and 12a.
Since the positive electrode 1 and the negative electrode 2 are
wound, the positive and negative electrode current
collector-exposed portions 11 and 12 are bent inward.
[0066] The positive electrode current collector plate 8 is abutted
on the flat portion 11a having a flux-coated layer formed on the
surface thereof. The positive electrode current collector plate 8
is heated using a non-contact heat source from the surface opposite
the surface thereof abutting on the flat portion 11a. Thus, the
positive electrode current collector plate 8 is welded to the flat
portion 11a of the positive electrode current collector-exposed
portion 11. Examples of welding using a non-contact heat source
include arc welding such as TIG welding, laser beam welding, and
electron beam welding. In terms of working efficiency and uniform
current collection, it is preferable that welding is performed
while moving a non-contact heat source 15 radially from above the
disc-shaped positive electrode current collector plate 8 (from
above the surface opposite the surface abutting on the positive
electrode current collector-exposed portion 11) as shown in FIG. 2.
The negative electrode current collector plate 9 is welded to the
flat portion 12a of the negative electrode current
collector-exposed portion 12 in the same manner as in the case
where the positive electrode current collector plate 8 is welded to
the flat portion 11a of the positive electrode current
collector-exposed portion 11.
[0067] In the above-described embodiment, a case was described
where the flux is applied to the surface of the positive electrode
current collector-exposed portion abutting on the positive
electrode current collector plate. However, the flux may be applied
to the surface of the positive electrode current collector plate
abutting on the positive electrode current collector-exposed
portion, or the flux may be applied to both of the surface of the
positive electrode current collector-exposed portion abutting on
the positive electrode current collector plate and the surface of
the positive electrode current collector plate abutting on the
positive electrode current collector-exposed portion.
Examples
[0068] Examples of the present invention will be described in
detail below, but the invention is not limited to these
examples.
Example 1
[0069] A cylindrical lithium secondary battery having the structure
shown in FIG. 1 as described above was produced in the following
manner.
(1) Production of Positive Electrode
[0070] Lithium cobaltate powder (average particle diameter of 10
.mu.m) as a positive electrode active material, acetylene black
(average particle diameter of 35 .mu.m) as a conductive material,
polyvinylidene fluoride (hereinafter, referred to as "PVDF") as a
binder were mixed in a weight ratio of 85:10:5 to yield a positive
electrode mixture. This positive electrode mixture was applied to
both sides of a 15 .mu.m-thick, 56 mm-wide strip-shaped positive
electrode current collector 1b made of aluminum foil, and then
dried to form a positive electrode active material layer 1a. At
this time, a portion where the positive electrode mixture was not
applied (current collector-exposed portion 11) was provided at one
widthwise end of the positive electrode current collector 1b. The
portion where the positive electrode mixture was applied (positive
electrode mixture-coated portion) was rolled to produce a 100
.mu.m-thick strip-shaped positive electrode 1. At this time, in the
width direction of the positive electrode 1, the width of the
positive electrode mixture-coated portion was 50 mm, and the width
of the positive electrode mixture-uncoated portion (current
collector-exposed portion 11) was 6 mm.
[0071] A slurry prepared by dispersing a non-corrosive flux
("NOCOLOK" (registered trademark), manufactured by Rio Tinto Alcan
Inc.) in water was applied to a portion of the end edge of the
current collector-exposed portion 11 extending from the end edge in
a width of 1 mm of the width (6 mm) of the positive electrode
mixture-uncoated portion (current collector-exposed portion 11),
and then heated at 100.degree. C. for 5 minutes to remove water.
Thus, a flux-coated layer was formed on the end edge of the
positive electrode current collector-exposed portion 11. At this
time, the amount of the flux applied was 0.2 g/cm.sup.2.
(2) Production of Negative Electrode
[0072] Artificial graphite powder (average particle diameter 15
.mu.m) as a negative electrode active material and PVDF as a binder
were mixed in a weight ratio of 95:5 to yield a negative electrode
mixture. This negative electrode mixture was applied to both sides
of a 10 .mu.m-thick, 57 mm-wide strip-shaped negative electrode
current collector 2b made of copper foil, and then dried to form a
negative electrode active material layer 2a. At this time, a
portion where the negative electrode mixture was not applied
(current collector-exposed portion 12) was provided at one
widthwise end of the negative electrode current collector 2b. The
portion where the negative electrode mixture was applied (negative
electrode mixture-coated portion) was rolled to produce a 100
.mu.m-thick strip-shaped negative electrode 2. At this time, in the
width direction of the negative electrode 2, the width of the
negative electrode mixture-coated portion was 52 mm, and the width
of the negative electrode mixture-uncoated portion (current
collector-exposed portion 12) was 5 mm.
(3) Production of Electrode Group
[0073] A strip-shaped separator 3 (having a width of 53 mm and a
thickness of 25 .mu.m) made of a microporous polypropylene resin
film was disposed between the positive electrode mixture-coated
portion and the negative electrode mixture-coated portion.
Thereafter, the positive electrode, the negative electrode, and the
separator were spirally wound to produce an electrode group 10. At
this time, separators 3 were also disposed on the outermost
circumference side and on the innermost circumference side of the
electrode group 10.
(4) Production of Current Collector Plate
[0074] A 50 mm-square aluminum plate (A1050) (thickness of 1 mm)
was pressed into a disc with a diameter of 24 mm to give a positive
electrode current collector plate 8. In addition, a hole with a
diameter of 7 mm was formed in the center of the aluminum disk.
[0075] A 50 mm-square copper plate (C1020) (thickness of 0.6 mm)
was pressed into a disc with a diameter of 24 mm to give a negative
electrode current collector plate 9.
(5) Production of Electrode Structure
[0076] The electrode group 10 was inserted into a specific
cylindrical molding tool having a bottom, and then pressed by a
specific pressing tool from the opening of the molding tool. At
this time, the end edges of the current collector-exposed portions
11 and 12 of the positive and negative electrodes were bent inward,
and thereby flat portions 11a and 12a were formed.
[0077] The positive electrode current collector plate 8 was abutted
on the flat portion 11a of the current collector-exposed portion 11
where the flux-coated layer was formed, and the positive electrode
current collector plate was TIG-welded to the flat portion 11a of
the positive electrode current collector-exposed portion 11. More
specifically, as shown in FIG. 2, using an arc welding machine (a
full digital AC/DC TIG welding machine 300BP2, manufactured by
Panasonic Welding Systems Co., Ltd.) as a non-contact heat source
15, an arc was applied to the upper surface of the positive
electrode current collector plate 8 while moving the non-contact
heat source 15 radially from above the positive electrode current
collector plate 8 (from above the surface opposite the surface
abutting on the positive electrode current collector-exposed
portion 11). The conditions of the TIG welding for the positive
electrode 1 side were a current value of 150 A and a welding time
of 100 ms. The negative electrode current collector plate 9 was
abutted on the flat portion 12a of the current collector-exposed
portion 12 of the negative electrode 2, and the flat portion 12a of
the negative electrode current collector-exposed portion 12 was
TIG-welded to the negative electrode current collector plate 9 in
the same manner as described above. The conditions of the TIG
welding for the negative electrode 2 side were a current value of
200 A and a welding time of 50 ms. Thus, an electrode structure was
produced.
(6) Production of Cylindrical Lithium Ion Secondary Battery
[0078] One end of the aluminum positive electrode connector piece
8a was laser-welded to the positive electrode current collector
plate 8 of the electrode structure. One end of the copper negative
electrode connector piece 9a was laser-welded to the negative
electrode current collector plate 9 of the electrode structure.
Thereafter, the electrode structure was housed in the cylindrical
battery can 5 having a bottom, and then the other end of the
negative electrode connector piece 9a was resistance-welded to the
inner bottom surface of the battery can 5. The other end of the
positive electrode connector piece 8a was laser-welded to the
battery cover 6.
[0079] Subsequently, the battery can 5 was dried by heating, and a
non-aqueous electrolyte was then injected into the battery can 5.
As the non-aqueous electrolyte, a non-aqueous electrolyte prepared
by dissolving lithium hexafluorophosphate (LiPF.sub.6) in a mixed
solvent of ethylene carbonate and ethylmethyl carbonate (volume
ratio 1:1) was used. Thereafter, the peripheral edge of the battery
cover 6 was crimped to the end of the opening of the battery can 5
with the resin sealing body 7 disposed therebetween. Thus, the
electrode structure was housed in a hermetically sealed manner in
the battery container 4 composed of the battery can 5 and the
battery cover 6 to produce a cylindrical lithium ion secondary
battery (battery capacity of 2600 mAh) with a diameter of 26 mm and
a height of 65 mm.
Comparative Example 1
[0080] A cylindrical lithium secondary battery was produced in the
same manner as in Example 1 except that the non-corrosive flux was
not applied to the positive electrode current collector-exposed
portion.
[Evaluation]
(1) Measurement of Tensile Strength
[0081] Five pieces of each battery of Example 1 and Comparative
Example 1 were provided. The tensile strength of the portion where
the positive electrode current collector plate and the positive
electrode are welded to each other of each battery was measured in
accordance with JIS Z 2241. Specifically, while the electrode group
was held on one side of a tensile tester (with a load cell SL-5001
and a displacement meter SL-100, manufactured by IMADA SEISAKUSHO
CO., LTD.), the positive electrode current collector plate was held
on the other side of the tensile tester. The electrode group and
the positive electrode current collector plate were pulled in the
axial directions of the tensile tester (the directions in which the
electrode group and the current collector plate moved away from
each other) at a constant speed, and the load with which the welded
portion failed and the positive electrode current collector plate
was separated from the portion where it was bonded to the electrode
group was regarded as a tensile strength.
[0082] All of the batteries of Example 1 had a tensile strength of
70 N or greater. On the other hand, three of the five batteries of
Comparative Example 1 had a tensile strength of 20 N or less, and
the welded portion failed.
(2) Measurement of Internal Resistance of Batteries
[0083] Fifty pieces of each battery of Example 1 and Comparative
Example 1 were provided. Each battery was subjected to three
repeated charge/discharge cycles in each of which the battery was
charged with a constant current of 1250 mA until the closed-circuit
voltage reached 4.2 V and then discharged with a constant current
of 1250 mA until the closed-circuit voltage reached 3.0 V.
Thereafter, an alternating current of 1 kHz was applied to each
battery to measure the internal resistance. Then, the average value
for and the variation in the internal resistance were determined.
The ratio of the maximum value (absolute value) of the difference
between a measured value and the average value relative to the
average value was used as the variation.
[0084] For the batteries of Example 1, the average value of the
internal resistance was 5 m.OMEGA., and the variation was 10%. On
the other hand, for the batteries of Comparative Example 1, the
average value of the internal resistance was 11 m.OMEGA., and the
variation was 20%.
[0085] The average output current (I) was calculated from the
measured internal resistance value (R) of each battery.
Specifically, the average output current in the case of charging a
battery until the closed-circuit voltage reached 4.2 V and then
discharging the battery until the closed-circuit voltage reached
1.5 V was calculated according to the equation: I (Average output
current)=2.7 V (Voltage)/R (Resistance).
[0086] The average value of the output currents of the batteries of
Example 1 was 540 A, whereas that of the batteries of Comparative
Example 1 was 245 A. This showed that the batteries of Example 1
can be discharged with a larger current than the batteries of
Comparative Example 1.
(3) Battery Vibration Test
[0087] Three pieces of each battery of Example 1 and Comparative
Example 1 were provided. Each battery was subjected to a vibration
test in accordance with JIS D 1601.
[0088] None of the batteries of Example 1 showed any change in
voltage before and after the test, and the inspection of the
interior after disassembling the batteries did not show any
abnormality. On the other hand, two of the three batteries of
Comparative Example 1 showed a voltage of 0 volt after the test. As
a result of disassembling these batteries and inspecting the
interior thereof, it was confirmed that the portion where the
positive electrode current collector plate and the positive
electrode current collector-exposed portion had been welded to each
other failed. In addition, as a result of inspecting the interior
of the battery of Comparative Example 1 whose voltage after the
test was not 0 volt, it was confirmed that the welded area (the
region where the bonded state was maintained) of the battery was
smaller than that of the batteries of Example 1.
INDUSTRIAL APPLICABILITY
[0089] The lithium ion secondary battery of the present invention
can be suitably used as a power source of electronic devices
requiring high output, such as portable devices.
* * * * *